Engines may use boosting devices, such as turbochargers, to increase engine power density. However, engine knock may occur due to increased combustion temperatures. Knock is especially problematic under boosted conditions due to high charge temperatures. The inventors herein have recognized that utilizing an engine system with a split exhaust system, where a first exhaust manifold routes exhaust gas recirculation (EGR) to an intake of the engine, upstream of a compressor of the turbocharger, and where a second exhaust manifold routes exhaust to a turbine of the turbocharger in an exhaust of the engine, may decrease knock and increase engine efficiency. In such an engine system, each cylinder may include two intake valves and two exhaust valves, where a first set of cylinder exhaust valves (e.g., scavenge exhaust valves) exclusively coupled to the first exhaust manifold may be operated at a different timing than a second set of cylinder exhaust valves (e.g., blowdown exhaust valves) exclusively coupled to the second exhaust manifold, thereby isolating a scavenging portion and blowdown portion of exhaust gases. The timing of the first set of cylinder exhaust valves may also be coordinated with a timing of cylinder intake valves to create a positive valve overlap period where fresh intake air (or a mixture of fresh intake air and EGR), referred to as blowthrough, may flow through the cylinders and back to the intake, upstream of the compressor, via an EGR passage coupled to the first exhaust manifold. Blowthrough air may remove residual exhaust gases from within the cylinders (referred to as scavenging). The inventors herein have recognized that by flowing a first portion of the exhaust gas (e.g., higher pressure exhaust) through the turbine and a higher pressure exhaust passage and flowing a second portion of the exhaust gas (e.g., lower pressure exhaust) and blowthrough air to the compressor inlet, combustion temperatures can be reduced while improving the turbine's work efficiency and engine torque.
However, the inventors herein have recognized further issues as a result of operation with such systems. As one example, during engine operation, one or more valve systems may be degraded such that a valve becomes stuck in one position or an actual position of a valve is different than a commanded position. When the degraded or mispositioned valve is one of an EGR valve disposed in the EGR passage or a bypass valve disposed in bypass passage coupled between the scavenge exhaust manifold and the exhaust passage, a desired amount of EGR and/or blowthrough may not be delivered to the intake passage. Similarly, when a timing of the scavenge exhaust valves is different than commanded, the desired amount of EGR and/or blowthrough may not be delivered to the intake passage. As a result, engine efficiency and fuel economy may be reduced.
In one example, the issues described above may be addressed by a method, comprising: operating a first set of exhaust valves coupled to a first exhaust manifold at a different timing than a second set of exhaust valves coupled to a second exhaust manifold coupled to an exhaust passage; and diagnosing a position of a first valve positioned in a first passage coupled between an intake passage and the first exhaust manifold based on an output of a pressure sensor positioned in the first exhaust manifold. As one example, a position of a second valve positioned in a bypass passage coupled between the first exhaust manifold and the exhaust passage and a timing of the first set of exhaust valve may also be diagnosed based on the output of the pressure sensor. A pressure drop across the first valve and second valve and a timing of the first set of exhaust valves may be determined based on the output of the pressure sensor. When the pressure drop across the first valve or second valve, or the timing of the first set of exhaust valves, is different than expected, the identified valve may be mispositioned or degraded. As a result of this diagnosis, the identified valve may be commanded into a different position and/or an alternate valve may be adjusted to achieve desired operating conditions (such as a desired EGR flow or pressure in the first exhaust manifold). Thus, when one or more of these valves are degraded or mispositioned, adjusting an alternate valve or changing the commanded position of the mispositioned valve may compensate for the difference in pressure (or timing) and deliver the desired EGR flow or blowthrough amount to the intake passage. As a result, engine efficiency and fuel economy may be increased.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.